Field of the Invention
This invention relates to a lifting mast of an industrial truck that has two vertical rails separated laterally from each other that are connected with each other by means of at least two cross members, in which one of the two cross members is a bottom cross member that is located in the bottom area of the vertical rails and at least one additional cross member that is at a distance in the vertical direction of the lifting mast from the bottom cross member, in which a longitudinally displaceable lifting carriage provided with load handling means is located in the vertical rails, and, to raise and lower the lifting carriage on the vertical rails, the lifting mast is provided with a lifting cylinder device that is supported on the bottom cross member, in which the lifting cylinder device is operationally connected with lifting means that are fastened with a first end to the lifting carriage and with a second end to the lifting mast and are reversed on the lifting cylinder device.
Description of Related Art
Lifting masts of this type can be in the form of a single-section lifting frame (also called a simplex lifting frame) or in the form of a telescoping mast of a multi-section lifting frame, such as a duplex lifting frame, that includes one stationary mast and one telescoping mast, or a triplex lifting frame that includes one stationary mast and two telescoping masts. On lifting masts of this type, between the vertical rails of which a longitudinally displaceable lifting carriage equipped with load handling means is provided, a lifting cylinder device is provided that raises and lowers the lifting carriage on the vertical rails of the lifting mast. The lifting cylinder device is supported on the bottom cross member and is operationally connected with lifting means such as a lifting chain. The lifting means are fastened with a first end to the lifting carriage and with the second end to the lifting mast. The lifting means are also guided on the lifting cylinder device by means of a return pulley.
Known types of lifting masts are also used in the form of a stationary mast of a single-section lifting frame or as a telescoping mast of a multi-section lifting frame in which the two laterally separated vertical rails of the lifting mast are connected to each other by means of three cross members. A first cross member is in the form of a bottom cross member which is located in the bottom area of the vertical rails. An additional cross member is in the form of a top cross member that is located in the top area of the vertical rails. An additional cross member is in the form of a center cross member that is located in the vertical direction of the lifting mast between the bottom cross member and the top cross member. The bottom cross member supports the lifting cylinder device in the vertical direction. For this purpose, the lifting cylinder device can be supported with a cylinder base on the bottom cross member. The lifting cylinder device is fastened to the middle cross member which acts as an additional fastening point for the lifting cylinder device and optionally also performs the function of protecting the lifting cylinder device against buckling. The lifting means reversed on the lifting cylinder device are therefore fastened with the second end to the middle cross member. The middle cross member therefore absorbs the tractive force of the lifting means. On a lifting mast of this type, twice the amount of the tractive force of the lifting means is supported as a result of the reversal of the lifting means on the lifting cylinder device on the cylinder base and thus on the bottom cross member. The resulting high reaction force on the bottom cross member produces a high load, in particular a high bending load, in the bottom cross member, and a disadvantageous flux of force from the bottom cross member into the vertical rails. If the bottom cross member is connected with the vertical rails by a welded connection with corresponding weld seams, this frequently leads to a disadvantageous flux of force from the bottom cross member via the weld seams into the vertical rails. The middle cross member, to which the lifting means are fastened with the second end, is also subjected to a high load as a result of the tractive force of the lifting means. If the lifting cylinder device is also fastened to the middle cross member, the middle cross member must additionally absorb the forces of the fastening of the lifting cylinder device.
The prior art also includes types in which the stationary mast is a single-section lifting frame or a multi-section lifting frame in the form of a telescoping mast in which the two laterally separated vertical rails of the lifting mast are connected to each other by means of two cross members. A first cross member is in the form of a bottom cross member which is located in the bottom area of the vertical rails. An additional cross member is in the form of a top cross member which is located in the top area of the vertical rails. The bottom cross member supports the lifting cylinder device in the vertical direction. The lifting cylinder device can, for this purpose, stand upright with a cylinder base on the bottom cross member.
In one lifting mast of this type, the lifting means can be fastened with the second end to a cylinder head or a cylinder housing of the lifting cylinder device. In this case, a component that serves as an abutment for a chain latch of lifting means in the form of a lifting chain can be located on the cylinder head or the cylinder housing of the lifting cylinder device. In a configuration of this type, the tractive force of the lifting means is transmitted directly into the lifting cylinder device. When the lifting means are fastened in this manner with the second end to the cylinder head or the cylinder housing of the lifting cylinder device, the reaction force on the bottom cross member can be reduced, because the single amount of tractive force of the lifting means, which is transmitted directly into the cylinder head or the cylinder housing of the lifting cylinder device, is counteracted by twice the amount of the tractive force from the reversal of the lifting means. On a lifting mast of this type the bottom cross member is subjected to a lower load, although an additional force is applied to the lifting cylinder device. Because the lifting means are fastened with the second end at a distance from the longitudinal axis and, thus, from the axis of positive output of the lifting cylinder device to the cylinder head or the cylinder housing of the lifting cylinder device, the tractive force of the lifting means is discharged at an offset relative to the line of action of the lifting cylinder device, so that the lifting cylinder device must withstand not only the tractive force but also a torque applied by the tractive force. This can require a reinforcement of the cylinder housing, for example a reinforced wall thickness of the cylinder housing, and the sealing and guidance system of the telescoping piston rod of the lifting cylinder device must be designed to withstand the greater deformations of the lifting cylinder device.
In the embodiment cited above, a lifting mast used as the stationary mast of a single-section lifting frame or as the telescoping mast of a multi-section lifting frame, in which the two laterally separated vertical rails of the lifting mast are connected to each other by means of two cross members, in which a first cross member is in the form of a bottom cross member and an additional cross member is in the form of a top cross member, the lifting means can be fastened with the second end to one or both vertical rails. A component can thereby be located on the vertical rails, for example by welding, that serves as an abutment for a chain latch of lifting means in the form of a lifting chain. In an embodiment of this type, the tractive force of the lifting means is discharged directly into the vertical rail of the lifting mast. With a fastening of this type of the lifting means, with the second end to the vertical rail of the lifting mast, the reaction force on the bottom cross member cannot be reduced, because the bottom cross member supports double the amount of the tractive force of the lifting means as a result of the reversal of the lifting means on the lifting cylinder device. The resulting high reaction force on the bottom cross member causes a high load, in particular a high bending load, in the bottom cross member and a disadvantageous flux of force from the bottom cross member into the vertical rails. If the bottom cross member is connected with the vertical rails by a welded connection with corresponding weld seams, the result is a disadvantageous flux of force from the bottom cross member via the weld seams into the vertical rails.